Two blasts in quick succession killed six policemen and wounded 26 people in Hilla, south of Baghdad, police said.
The first blast occurred about 10.30pm on Saturday when a bomber detonated a belt of explosives while being searched by members of the elite Scorpion police command at a checkpoint in the centre of the city, according to Captain Muthana Khalid Ali of the Babil provincial press office.
Six policemen and the attacker died in the blast, Ali said.
About 10 minutes later, a second bomber blew himself up in a crowd of police and civilians who had rushed to the scene of the first blast, Ali said.
Twenty-six people were injured in the second explosion, according to Dr. Hashim Suleiman of the Hilla General Hospital.
Hilla is about 95km south of Baghdad.
Earlier during the day, a bomber strapped with explosives killed at least 17 people waiting outside a police recruiting centre for special forces in Iraq's capital.
There was confusion over the precise death count from the attack.
The al-Yarmuk Hospital reported receiving 17 dead and 22 wounded from the blast.
The dead included 11 recruits and six civilian bystanders, the hospital said. But Colonel Adnan Abdul-Rahman put the death toll at eight, down from his original count of 20.
He said the 20 figure was based on an erroneous preliminary report.
The US military said eight to 10 people died in the attack.
The bomber was dressed in the police commando uniform and was easily able to enter the headquarters, Walid Khalid, an Iraqi journalist, told Aljazeera.
A military statement said: "A terrorist reportedly walked into the crowd and detonated his vest, which was packed with ball bearings."
The Interior Ministry source said the bomber wore an explosive vest beneath civilian clothes when he approached the Interior Ministry's special forces recruitment centre in the Mansour district of western Baghdad.
At least 11 police recruits were
killed in Saturday's bomb attack
The recruitment centre, near the Green Zone government and diplomatic compound, has been targeted by bombers several times in the past.
An Interior Ministry source said recruits had been told to come on Saturday, normally a non-working day, in an effort to protect the volunteers.
Police Lieutenant-Colonel Anwar Sheik Kabeer Sorchyee was shot dead on Saturday as he drove to work in the northern city of Mosul, police said.
A bomb exploded on Saturday in a vegetable cart in a market in Mahmoudiya, a religiously mixed town about 20km south of Baghdad, killing two people and injuring 10 others, hospital officials said.
The blast occurred a few minutes after mourners passed by with the body of an aide to Shia Grand Ayat Allah Ali al-Sistani - Kamaleddin al-Ghuraifi - who was slain on Friday outside a Baghdad mosque.
Thousands mourned slain cleric
It was unknown whether the bomb was intended for the mourners, who were carrying the body through the town en route to burial in the Shia shrine city of Najaf.
"It is a calamity for the neighbourhood, for Baghdad, for Muslims and for Shia," al-Ghuraifi's weeping brother Abu Hussein said. "What was his guilt? He was an old man, 70 years old and paralysed. What did he do?"
Al-Ghuraifi's murder was one of three attacks on prominent Shia targets within 24 hours.
Tribal leader arrested
Also in Mahmoudiya, US troops arrested Shaikh Adnan Fahd, the head of the area's al-Ghrir tribe, according to his brother, Eissa Fahd. There was no comment from US officials.
Also on Saturday, al-Qaida in Iraq claimed responsibility for Friday's attack outside Prime Minister Ibrahim al-Jaafari's Islamic Dawa Party offices in Baghdad's Mansour district. The posting on an Islamic website could not be verified.
Most attacks have been blamed on Sunni Arab fighters seeking to destabilise the US-backed Iraqi government, which is dominated by Shia and Kurds.